The present invention relates to fluorescent lamp ignition circuits, and relates more particularly to such a fluorescent lamp ignition circuit which comprises a double-feedback loop that reduces the voltage of the circuit to earth to one half of the input voltage so as to minimize power loss.
FIG. 1 shows a fluorescent lamp ignition circuit according to the prior art. This fluorescent lamp ignition circuit comprises a DC voltage stabilizer 10', an inductance filter 20', an oscillator 30', and a feedback circuit 40'. The DC voltage stabilizer 10' processes 8-20 V voltage from Vin into a constant voltage by dropping or boosting, and then sends the processed constant voltage to the transformer of the oscillator 30' via the inductance filter 20'. The inductance filter 20 is to remove surge from power supply passing through and to store electric energy so as to provide the desired constant DC voltage to the oscillator 30'. The transformer of the oscillator provides a sin-wave output to the fluorescent lamp 50' by means of the oscillation induced between the inductor and the capacitor at its primary side, wherein the transistors Q1 and Q2 are for the switching between the positive half cycle and negative half cycle of the sin-wave. The feedback circuit 40' uses a resistor R to obtain output current I so as to provide a feedback voltage to the DC voltage stabilizer 10 for controlling the value of the input voltage. FIG. 2 shows the circuit of the transformer of the oscillator 30'. Because the circuit has only one end connected to earth, if the output voltage of the oscillator 30' is 375 V, the voltage of the circuit to earth is 375 V. Because the circuit is a high frequency circuit, drain current is produced, and the volume of drain current will be relatively increased when the frequency becomes higher. If to increase the brightness of the fluorescent lamp 50', the frequency must be relatively increased. However, when the frequency is increased, power loss will be relatively increased. FIG. 3 shows the relative curve between the collector current and the drain current at 31 KHz, 70 KHz, 100 KHz and 200 KHz. As indicated, when at a high frequency, much drain current is produced. Therefore, this fluorescent lamp ignition circuit cannot work properly at a high frequency level.